1. Field of the Invention
The invention relates to a reinforcing device in the inner portion (lead in) of seismic cables, especially cables that are towed laterally and displaced in parallel in relation to the towing vessel, wherein said cable is provided with at least two layers of reinforcement intended to absorb stretch loads.
2. Description of the Prior Art
When seismic cables are towed behind a vessel at sea the cable will be subjected to great stretch loads due to the movement through the water. This is especially true when the seismic cables are towed displaced in parallel in relation to the towing vessel, i.e. when, e.g. a number of parallel hydrophone cables or streamers are towed side-by-side. In such cases the inner portion of the cable, which is often designated the "lead in" stretch portion, will extend obliquely in relation to the towing direction to a fastening point for an otter board/paravane member, from which point the cable follows the towing direction. Said oblique inner portion of the cable is, thus, subjected to great forces both because it extends across the towing direction and is, thus, subjected to lateral forces, and because it is subjected to stretch forces from the buoyancy member and the otter board in addition to the extension of the cable itself.
A cable design with several outside layers of reinforcement, commonly two, is therefore used, especially in the inner portion of such cables. To achieve satisfactory transmission of forces at both ends of said inner portion, hitherto direct clamping of the cable, e.g. in a clamp block, provided in the angular fastener, was used, the cable being bent in the towing direction, and with additional clamping with a similar fastener in the fastening area at the towing vessel itself. These fastening methods were not satisfactory, and there were increasing problems with increasing efforts to use a larger number of cables or streamers, respectively, side-by-side in parallel, causing increasing lengths of the inner portion of the cable. Thus, friction and slip in the fasteners will easily result, rendering the towing conditions somewhat uncertain, and additionally, considerable damage to the main cable portion may result.